Comparison of arousal index, AHI and ODI during different sleep stages. The arousal index (A), AHI (B) and ODI (C) during different sleep stages were compared between OSA patients and controls. Data are expressed as median (horizontal lines), interquartile range (box) and range minimum to maximum (whiskers). *p<0.05, **p<0.01, ***p<0.001 vs control group. AHI, apnea/hypopnea index; N1, N2 and N3, non-REM sleep stage 1, stage 2 and stage 3; ODI, oxygen desaturation index; OSA, obstructive sleep apnea; R, rapid eye movement sleep (REM).